Histopathological Features of MRI‐Invisible Regions of Prostate Cancer Lesions

Abstract

Background Previous studies have reported tumor volume underestimation with multiparametric (mp)MRI in prostate cancer diagnosis. Purpose To investigate why some parts of lesions are not visible on mpMRI by comparing their histopathology features to those of visible regions. Study Type Retrospective. Population Thirty‐four patients with biopsy‐proven prostate cancer scheduled for prostatectomy (median 68.7 years). Field Strength/Sequence T2‐weighted, diffusion‐weighted imaging, T2 mapping, and dynamic contrast‐enhanced MRI on two 3T systems and one 1.5T system. Assessment Two readers delineated suspicious lesions on mpMRI. A pathologist delineated the lesions on histopathology. A patient‐customized mold enabled the registration of histopathology and MRI. On histopathology we identified mpMRI visible and invisible lesions. Subsequently, within the visible lesions we identified regions that were visible and regions that were invisible on mpMRI. For each lesion and region the following characteristics were determined: size, location, International Society of Urological Pathology (ISUP) grade, and Gleason subpatterns (density [dense/intermediate], tumor morphology [homogeneous/heterogeneous], cribriform growth [yes/no]). Statistical Tests With generalized linear mixed‐effect modeling we investigated which features explain why a lesion or a region was invisible on MRI. We compared imaging values (T2, ADC, and Ktrans) for these features with one‐way analysis of variance (ANOVA). Results Small, anterior, and ISUP grade 1–2 lesions (n = 34) were missed more frequent than large, posterior, ISUP grade ≥ 3 lesions (n = 35). Invisible regions on mpMRI had lower tumor density, heterogeneous tumor morphology, and were located in the transition zone. Both T2 and ADC values were higher in "intermediate" compared with "dense" regions (P = 0.002 and < 0.001) and in regions with heterogeneous compared with homogeneous morphology (P < 0.001 and 0.03). Ktrans was not significantly different (P = 0.24 and 0.99). Data Conclusion Regions of prostate cancer lesions that are invisible on mpMRI have different histopathology features than visible regions. This may have implications for monitoring during active surveillance and focal treatment strategies. Level of Evidence: 3 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2020;51:1235–1246.

Conspicuity of prostate cancer on multiparametric magnetic resonance imaging: A cross‐disciplinary translational hypothesis

“…Furthermore, it appears that cellular heterogeneity (eg, presence of acinar and foamy cell types) was found more frequently in mpMRI-invisible disease compared to mpMRI-visible disease, which tended to have more homogenous cell morphologies. 9 Finally, prostate tumors arising in the transitional zone of the prostate also had reduced visibility on mpMRI compared to those originating in the peripheral zone, which had greater visibility. 9 These histopathological properties are informative, as Gleason grade, tumor volume, tumor cellular density, microvessel density, presence of cribriform and intraductal carcinoma, and tumors arising in the peripheral zone are all features associated with increased likelihood of disease recurrence following surgery.…”

“…9 Finally, prostate tumors arising in the transitional zone of the prostate also had reduced visibility on mpMRI compared to those originating in the peripheral zone, which had greater visibility. 9 These histopathological properties are informative, as Gleason grade, tumor volume, tumor cellular density, microvessel density, presence of cribriform and intraductal carcinoma, and tumors arising in the peripheral zone are all features associated with increased likelihood of disease recurrence following surgery. [26][27][28][29][30][31] As such, these pathological observations further suggest that tumor mpMRI visibility may have genuine prognostic utility.…”

“…Compared to invisible disease, mpMRI‐visible tumors appear to have higher Gleason grading, 1,22 and increased tumor volume, cellular density, 23,24 microvessel density, and proportion of unusual aggressive subtypes (such as, cribriform 9,25 and intraductal carcinoma). Furthermore, it appears that cellular heterogeneity (eg, presence of acinar and foamy cell types) was found more frequently in mpMRI‐invisible disease compared to mpMRI‐visible disease, which tended to have more homogenous cell morphologies 9 . Finally, prostate tumors arising in the transitional zone of the prostate also had reduced visibility on mpMRI compared to those originating in the peripheral zone, which had greater visibility 9 …”

“…7 Cribriform pattern cancer is closely associated with Gleason grade (specifically, Gleason grade 4) and is noted to have increased mitotic rate, vascular invasion, tissue necrosis, 58 and association with distant metastasis and disease-specific mortality, 58,59 which are all features suggestive of mpMRI-visible disease. 1,9 Furthermore, tumor necrosis and low oxygenation levels (features found in cribriform cancer) are related to tumor size, which is another strong correlate of tumor visibility. 1,60 Overall, it seems that the small number of studies that report aggressive cribriform cancer to be an mpMRI-invisible entity 56 may be outweighed by a higher number of studies which demonstrate that most tumors containing this cancer subtype are visible on mpMRI.…”

Value of an online PI-RADS v2.1 score calculator for assessment of prostate MRI

“…As cost of care and efficacy have increasingly become important factors in healthcare in general, reporting time has become an important performance indicator. Second, lesion morphology very often tends to be visually equivocal, presumably due to (i) a generally small size of the target and (ii) inherent technical difficulties to visualize such a lesion on MRI [6], thereby leaving room for subjectivity. At the same time 'quantification' of features and semiquantitative metrics are not currently integrated in PI-RADS v2.1 in order to keep the reporting process as simple as possible.…”